1. Field of the Invention
The present invention relates to a heat exchanger with small-diameter refrigerant tubes and, more particularly, to a heat exchanger designed such that the number, shape and dimension of vertical slits formed on its air guide fins are optimally designed to be compatible with the small-diameter refrigerant tubes.
2. Description of the Prior Art
FIG. 1 is a perspective view of a conventional heat exchanger. FIG. 2 is a perspective view of a conventional air guide fin for such heat exchangers. FIG. 3 is a sectional view of the conventional air guide fin taken along the line Axe2x80x94A of FIG. 2.
As shown in FIG. 1, the conventional heat exchanger comprises a plurality of refrigerant tubes 1 and a plurality of air guide fins 3. The refrigerant tubes 1 form a refrigerant passage of the heat exchanger, while the air guide fins 3 are vertically arranged at regular intervals, with the linear parts of the refrigerant tubes 1 passing through the fins 3. The air guide fins 3 secure the heat exchange surface for allowing heat transfer between refrigerant and atmospheric air, and improve heat exchange efficiency of the heat exchanger.
In the conventional heat exchanger, the entire refrigerant tubes 1 are arranged relative to the air guide fins 3 to form two vertical rows of tubes: left- and right-hand vertical rows of tubes 1a and 1b as best seen in FIG. 1. Each of the air guide fins 3 thus has two vertical rows of tube-fitting openings 20 for allowing an installation of the tubes 1a and 1b. 
As shown in FIGS. 2 and 3, each of the air guide fins 3 is typically provided with a plurality of vertical slits 10 for allowing air to pass through and enhancing the heat exchange efficiency of the heat exchanger.
In order to form the slits 10 on each air guide fin 3, the fin 3 is pressed at regularly spaced positions to form a plurality of offset surfaces 10a such that the offset surfaces 10a are alternately offset in opposite directions as best seen in FIG. 3. Two air guide openings are thus formed between opposite side edges of each offset surface 10a and the land surface of the fin 3, and allow air to smoothly pass through to improve heat exchange effect of the heat exchanger.
In a detailed description with reference to FIGS. 2 and 3, a set of vertical slits 10 are each vertically formed on the fin 3 at a position between two tube-fitting openings 20 of each vertical row of openings 20 through a pressing process. In such a case, six rows of vertical slits 10 are arranged in a transverse direction of the fin 3 at a position between the two tube-fitting openings 20. The slits 10 are formed by the air guide openings, each of which is defined between opposite side edges of each of the offset surfaces loa and the land surface of the air guide fin 3.
Of the six rows of vertical slits 10, the first, third and fifth rows of slits 11, 13 and 15 are formed by the upward offset surfaces 11a, 13a and 15a, while the second, fourth and sixth rows of slits 12, 14 and 16 are formed by the downward offset surfaces 12a, 14a and 16a. In such a case, the terms xe2x80x9cupward offsetxe2x80x9d and xe2x80x9cdownward offsetxe2x80x9d are defined from FIG. 3 for ease of description. The first row of slits 11 comprise three unit slits vertically spaced apart from each other, while the second and sixth rows of slits 12 and 16 each comprise two unit slits vertically spaced apart from each other.
When the slits 10 are formed on each of the air guide fins 3 as described above, the slits 10 reduce the thickness of the thermal boundary layer inside the atmospheric air flowing along the fins 3, thus increasing the average heat transfer coefficient of air, and improving heat exchange operational performance of the heat exchanger.
The conventional heat exchanger is designed to use refrigerant tubes 1 having an outer diameter of 7 mm or 9.52 mm. In recent years, it is desired to reduce the outer diameter of the refrigerant tubes 1 in an effort to accomplish a preferable reduction in both the production cost and air-side pressure loss of heat exchangers. The refrigerant tubes 1 having such a reduced outer diameter are so-called xe2x80x9csmall-diameter refrigerant tubesxe2x80x9d in the specification.
When a heat exchanger uses a plurality of small-diameter refrigerant tubes having a reduced outer diameter in place of conventional refrigerant tubes 1 having an outer diameter of 7 mm or 9.52 mm, it is necessary to optimally design the arrangement and shape of both the air guide fins 3 and the slits 10 so as to allow the fins 3 and the slits 10 to be compatible with the small-diameter tubes 1.
When a heat exchanger is fabricated using the small-diameter refrigerant tubes 1 and the air guide fins 3 without changing the arrangement and shape of the fins 3, it is almost impossible to form the slits 10 on the fins 3 since the widths of the slits 10 are extremely reduced as the width of the fins 3 is reduced due to the reduced outer diameter of the refrigerant tubes 1.
In the case of using such small-diameter refrigerant tubes 1 in a heat exchanger, the heat exchange efficiency of the air guide fins 3 may be deteriorated since the heat exchange surface area of each fin 3 is reduced due to a reduction in the width of the fin 3. In the prior art, such deterioration in the heat exchange efficiency of the fins 3 may be overcome by increasing the number of the air guide fins 3 per unit length of the refrigerant tubes 1 to compensate for the reduction in the heat exchange surface area of the fins 3. However, when a plurality of slits having the same arrangement and shape as those of the conventional slits 10 are formed on such fins 3, the air-side pressure loss of the heat exchanger is extremely increased to undesirably eliminate the advantages expected from the use of the small-diameter tubes as the refrigerant tubes.
That is, when a heat exchanger is fabricated using such small-diameter refrigerant tubes 1 while densely arranging the air guide fins 3 each having the six rows of vertical slits 10 in a conventional manner, the fins 3 undesirably increase resistance against air to overload a blower fan, thus damaging or breaking the blower fan.
Therefore, it is necessary to propose an air guide fin, which is preferably used in a heat exchanger having small-diameter refrigerant tubes, and of which the slits are appropriately arranged, shaped and sized to be compatible with the small-diameter refrigerant tubes.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a heat exchanger with small-diameter refrigerant tubes, of which the number, shape and dimension of vertical slits formed on the air guide fins are optimally designed to be compatible with the small-diameter refrigerant tubes, and which thus minimizes its airside pressure loss, in addition to accomplishing an improvement in the heat transfer efficiency of the fins.
In order to accomplish the above object, the present invention provides a heat exchanger, comprising a plurality of air guide fins securing a heat exchange surface for allowing heat transfer between refrigerant and atmospheric air and assembled with each other by one or more vertical rows of refrigerant tubes passing through the air guide fins, wherein each of said refrigerant tubes is a small-diameter tube having an outer diameter of not larger than 6 mm; and four rows of offset surfaces vertically formed on each of said air guide fins at a position between two tubes of each vertical row of refrigerant tubes through a pressing process such that the four rows of offset surfaces are arranged along a transverse direction of said fin, with four rows of vertical slits each formed by two air guide openings defined between opposite side edges of each of said offset surfaces and the land surface of the air guide fin.